Friction plates for use in a clutch are generally manufactured by bonding friction material, often paper-based, to both sides of a steel core plate using an adhesive, often a phenolic resin which is baked in a press. Grooves for cooling oil may be formed in the friction plate by pressing, grinding, or by leaving material out in positions where grooves are desired.
Forming friction plates by bonding friction material to a steel core plate with adhesive may be expensive. The adhesive may cost as much as the friction material itself and the process for handling the adhesive is very sensitive. The adhesive is also flammable and hazardous and therefore requires special handling. Furthermore adhesives may have detrimental environmental impacts. Conditions must be maintained very accurately for each plate or durability and performance problems can occur, such as shudder and delamination, which occurs at the line of adhesive penetration into the friction material, or debonding failures. Using adhesive may also have a negative impact on the clutch environment.
U.S. Pat. No. 7,731,005 describes concentrically arranged friction materials integrally connected to each other. U.S. Pat. Pub 2013/0092499 describes a friction plate with friction paper without the use of adhesives. U.S. Pat. Pub 2014/0144747 A1 describes a friction plate having mechanically connected friction material. U.S. Pat. Pub 2014/0326573 A1 describes a friction plate including connected core plates.